1. Field of the Invention
This invention relates generally to joystick devices of the kind having a swivel mounted manually-engageable lever capable of movement from a center position to any one of a number of angular positions lying within a theoretical upwardly-extending conical surface, for controlling the operation of various types of electronic or electromechanical equipment.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
In the past a number of arrangements have been proposed and produced for converting the mechanical movements of a pivoted control lever into electrical output signals suitable for controlling various kinds of electrical circuits or electro-mechanical devices.
U.S. Pat. No. 4,284,885 issued Aug. 18, 1981 illustrates one such device, described in the patent as an optical potentiometer. A lever which is pivoted on a base carries a disk-like member having two arcuate portions of variable opacity. The portions lie along a common radius, and there is a space between their adjacent ends, to provide a "dead" spot or dwell. A light bulb is mounted on one side of the disk-like member, with a phototransistor on the opposite side. As the disk moves with the lever, the amount of light received by the phototransistor varies with the lever's position, producing an input/output response curve as shown in FIG. 9 of the patent.
While such an arrangement is relatively simple in its construction, variations in the output intensity of the source, as well as in the response of the phototransistor have been found to introduce serious errors. These variations can take the form of changes in the devices resulting from aging, clouding of the translucent portion from dirt, dust, etc., or from deterioration of the material of which the translucent portion is constituted. In addition, major response deviations have been found to occur with variations in temperature. In particular, the drift associated with incandescent bulbs, light-emitting diodes and transistors is well known, and recognized as a significant problem which has to be considered in any electronic design incorporating such devices.
U.S. Pat. No. 4,514,600 issued Apr. 30, 1985 shows a joystick construction which employs four contact pads that are adapted to be engaged by a spring which is carried by a manually-engageable lever swivel-mounted on a base. Through the use of four pads, movement of the lever toward any one of eight 45.degree. segments can be detected, as indicated by the markings on the face of the housing in FIG. 1 of the patent.
A considerably more sophisticated joystick control is illustrated in U.S. Pat. No. 4,161,726 issued July 17, 1979. This patent discloses a "digital" joystick which incorporates pivotally-mounted printed circuit board sectors that move with the lever and have defined contact areas adapted to be engaged by projecting fingers on cooperable stationary insulating boards which are disposed parallel to but radially outside the moving circuit boards. The arrangement of the conductors on the pivoted boards, together with the locations of the fingers on the stationary insulating boards, determines the response of the device as the lever is actuated. Depending on the particular geometry of the contacting areas, relatively complicated de-coding circuitry is required in order to provide the desired output signals.
Still other types of previously known joysticks have incorporated carbon composition or wire-wound potentiometers mounted at right angles, and adapted to be turnably driven in response to movement of the joystick lever. In general this type of arrangement suffered from the following disadvantages. Carbon potentiometers are notoriously noisy, and usually exhibit contact inconsistencies over much of the range of adjustment. In addition they tend to wear easily. This problem is especially troublesome with joystick controls, since the potentiometer is usually being driven over a very small portion of its range, namely that near its center of travel. The repeated transitions over this central area eventually lead to erratic operation. Wire wound potentiometers suffer some of the same drawbacks as regards wear and noise. In addition, the resolution is often limited, since the wiper contact moves in steps wherein adjacent turns of the toroidal coil are successively bridged.
Finally where it is desired to employ a joystick in an industrial application, the use of mechanical contacts can constitute a distinct disadvantage, as for example where there are present various gases or vapors that are potentially explosive. Such devices also present problems in installations where there exists other relatively sensitive equipment in the vicinity of the joystick, where the make-and-break nature of a mechanical potentiometer can generate static or noise (radio frequency interference) that adversely affects the operation of such equipment.